Mobile unit for self-propelled irrigation systems

ABSTRACT

A mobile unit for self-propelled irrigation systems having a plurality of mobile units wherein each mobile unit has an elongate frame, a yoke mounted on each end of the frame, a wheel rotatably mounted on each of the yokes, an elongate irrigation pipe has one end mounted on and extends transversely from one side of the frame, truss members supporting the irrigation pipe, and drive means operatively connected thereto for driving the mobile unit. The mobile units in the irrigation system are adapted to move relative to each other by a slip or expansion joint having one end of a slip joint pipe received in one end of a sleeve member mounted in the frame and one end of the irrigation pipe communicating with the other end of the sleeve member. A collar is mounted on the other side of the frame and has fluidtight seal means therein engaging an exterior surface of the slip joint pipe whereby the slip joint pipe can move relative to the frame. Movement limiting means extend between the other end of the slip joint pipe and the other side of the frame for maintaining the one end of the slip joint pipe within the sleeve member.

United States Patent [72] lnventor [21 1 App]. No. [22] Filed [45Patented [54] MOBILE UNIT FOR SELF-PROPELLED IRRIGATION SYSTEMS 7Claims, 8 Drawing Figs.

3,379,378 4/1968 Kern 239/212 3,394,729 7/1968 Bower et a1. 137/3443,417,766 12/1968 Purtell 137/344X 3,447,751 6/1969 Wieck 239/212Primary Examiner-Samuel Scott Altomey- Fishburn, Gold and LitmanABSTRACT: A mobile unit for self-propelled irrigation systems having aplurality of mobile units wherein each mobile unit has an elongateframe, a yoke mounted on each end of the frame, a wheel rotatablymounted on each of the yokes, an

elongate irrigation has one end mounted on and extends Int. transverselyfrom one ide of the frame truss members sup- Eolh 3/02 porting theirrigation pipe, and drive means operatively con- Field of Search nectedthereto for driving the mobile unit The mobile units in 39/212,213 theirrigation system are adapted to move relative to each other by a slipor expansion joint having one end of a slip joint [56] References cuedpipe received in one end of a sleeve member mounted in the UNITED STATESPATENTS frame and one end of the irrigation pipe communicating with1,346,843 7/1920 Ramen 239/213 the other end of the sleeve member. Acollar is mounted on 2,796,292 6/1957 Maggart 239/213 the other side ofthe frame and has fluidtight seal means 2,800,364 7/1957 Dick et al.239/212X therein engaging an exterior surface of the slip joint pipe2,834,634 5/1958 Johnson 239/213X whereby the slip joint pipe can moverelative to the frame. 3,202,172 8/1965 Bergeron et al. 137/344 Movementlimiting means extend between the other end of 3,355,109 1 1/1967 Kane137/344X the slip joint pipe and the other side of the frame formaintain- 3,360,200 12/1967 Purtell 239/213 ing the one end of the slipjoint pipe within the sleeve member. i

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2.4 Z3 i 16 36 T 37 PATENTEU MAR 2197:

SHEET 1 BF 3 mm QM ATTORNEYS INVENTOR. BENJAMIN P1. NEIER ATTORNEYSMOBILE UNIT FOR SELF-PROPELLED IRRIGATION SYSTEMS This invention relatesto self-propelled irrigation systems and more particularly to a mobileunit for such irrigation systems.

The principal objects of the present invention are: to provide a novelmobile unit for self-propelled irrigation systems having a plurality ofsimilar mobile units wherein the irrigation system is radiallyextendible and contractible; to provide such a mobile unit having anovel truss structure supporting an irrigation pipe extendingtransversely from one side of a mobile frame; to provide such a mobileunit wherein the irrigation pipe is cambered or bowed upwardly to resistthe weight of an irrigation fluid moving therethrough; to provide such amobile unit having a slip or expansion joint permitting the mobile unitto travel over uneven terrain and to precede or trail adjacent mobileunits; to provide such a slip joint in such a mobile unit wherein themobile unit may move toward and away from adjacent mobile unit may movetoward and away from adjacent mobile units thereby shortening orlengthening the irrigation system; to provide such a mobile unit havinga slip joint pipe having one end movably received in the slip orexpansion joint and extending transversely from the other side of themobile unit and movement limiting means extending between the other endof the slip joint pipe and the other side of the mobile frame formaintaining the one end of the slip joint pipe within the slip orexpansion joint; and to provide such a mobile unit which is economicalto manufacture, easily maintained, simple to operate, positive andefficient in operation, and particularly well adapted for the proposeduse.

Other objects and advantages of this invention will become apparent fromthe following description taken in connection with the accompanyingdrawings wherein are set forth by way of illustration and examplecertain embodiments of this invention.

FIG. I is a front elevational view of a mobile unit, embodying featuresof the present invention, for use in self-propelled irrigation systemshaving a plurality of similar units with portions of adjacent unitsshown in broken lines.

FIG. 2 is a side elevational view of the mobile unit.

FIG. 3 is a fragmentary perspective view of the drive means for themobile unit.

FIG. 4 is an enlarged fragmentary sectional view taken on line 4-4, FIG.1, showing a movement permitting expansion joint means.

FIG. 5 is a transverse sectional view taken on line 5-5, FIG. 1, showinga center truss frame.

FIG. 6 is an enlarged fragmentary sectional view taken on line 6-6, FIG.1, showing a frame clamp on ends of intermediate truss frames.

FIG. 7 is an enlarged fragmentary sectional view taken on line 7-7, FIG.1, showing a frame clamp on ends of end truss frames.

FIG. 8 is an enlarged fragmentary sectional view taken on line 8-8, FIG.1, showing a'truss rod connector clamp.

Referring more in detail to the drawings:

The reference numeral 1 generally designates a mobile unit for use inself-propelled irrigation systems having a plurality of similar mobileunits radially spaced along and supporting an elongate irrigation pipe 2which is connected to a central water supply pipe (not shown) whereinthe mobile units are driven to move the irrigation pipe 2 in an area tobe irrigated either in a straight line or around the central supply pipe(not shown) as an axis.

Each mobile unit I has a mobile frame 3 supporting the elongateirrigation pipe 2 extending transversely from one side .of the mobileframe 3 and supported by a truss structure 4. An elongate slip jointpipe 5' has one end movably received in a slip or expansion joint 6 andextends transversely from the other side of the mobile frame 3. Theother end of the slip joint pipe 5 is connected to an adjacent mobileunit I whereby the mobile unit I may move relative to adjacent mobileunits l' on each side thereof. Movement limiting means 7 extend betweenthe other end of the slip joint pipe 5' and the other side of the mobileframe 3 for maintaining the one end of the slip joint pipe 5' within theslip or expansion joint 6.

The mobile frame 3 has a substantially triangular unit frame 8 which hasan elongate base member 9 and elongate side members 10 and 11. The basemember 9 is substantially parallel with a ground surface 12 traveled bythe mobile unit I and the side members 10 and 11 each have one endconnected to and extend upwardly from the opposite ends of the basemember 9 and are joined together at their other or upper ends with theslip or expansion joint 6 mounted at theupper ends of the side members10 and 11 or adjacent the apex of the triangle formed by base member 9and the side members 10 and 11. A pair of longitudinally spaced yokes l4and 15 are mounted on opposite ends of the base member 9 and dependtherefrom. The yokes l4 and 15 each have ground engaging elements 16 and17 respectively rotatably mounted therein.

In the illustrated structure, the yokes l4 and 15 each have a webportion 18 suitably secured to the base member 9, as by bolts 19, andspaced legs 20 and 21 extending downwardly from opposite edges of theweb portion 18. The ground engaging elements 16 and 17 are illustratedas wheels each having an axle 22 rotatably mounted in lower edgeportions 23 of the legs 20 and 21, as by suitable bearings 24.

Drive means including a suitable motor, is operatively connected to theground engaging elements 16 and 17 for driving the mobile unit 1. Whilethe motor may be electric, in the illustrated structure, it is hydraulicand the hydraulic motor 25 receives fluid under pressure from a suitablesource, such as a motor driven pump, (not shown). The motor 25 isoperative to rotate a drive shaft 26 having a pair of spaced drive gears27 and 28 mounted thereon intermediate the ends thereof. Suitable powertransmitting members, such as endless chains 29 and 30, engage the drivegears 27 and 28 respectively and are operative to rotate sprockets 31and 32 mounted on shafts 33 and 34 rotatably mounted in the yokes I4 and15 respectively, as by bearings 35 mounted in the legs 20 and 21 of therespective yokes I4 and 15. A sprocket 36 is mounted on each of theshafts 33 and 34 intermediate the ends thereof and is positioned to havethe teeth of the sprocket 36 enter circumferentially spaced recesses 37in the periphery or rim 38 of the respective wheels 16 and I7 wherebythe mobile unit 1 is driven by the hydraulic motor 25.

The irrigation pipe 2 has one end mounted on one side of the unit frame3 and extends transversely therefrom and in the illustrated structure,the irrigation pipe 2 has a plurality of pipe sections 39 each having aflange 40 at opposite ends thereof and the pipe sections 39 are joinedtogether by a plurality of suitable fastening devices, such as bolts 41,extending through the flanges 40 on adjacent pipe sections 39. Bolts 42mount the flange 40 at the one end of the irrigation pipe 2 to the oneside of the unit frame 3. Each irrigation pipe section 39 has at leastone suitable sprinkler head 43 mounted therein for distributing theirrigation fluid, such as water or water and selected chemicals, overthe ground surface 12 traveled by the mobile unit 1.

The irrigation pipe 2 and the truss structure 4 supporting same are eachon one side of the mobile unit I and the truss structure 4 includes aplurality of elongate truss frames 44 mounted on the irrigation pipesections 39 and depending therefrom. The truss frames 44 arelongitudinally spaced along the irrigation pipe 2 and each issubstantially parallel with the triangular unit frame 8. The trussframes 44 are engaged by tension members 45 and 46 at opposite endsthereof. The tension members 45 and 46 each have one end mounted on theone side of the unit frame 8 and engage each of the truss frames 44 atthe opposed ends thereof. The other ends of the tension members 45 and46 are mounted on a slip joint pipe 5 of the mobile unit 1, as laterdescribed.

The truss frames 44 are each illustrated as substantially triangularshaped structures each having an elongate base member 47 which ispositioned substantially parallel with the ground surface 12 and sidemembers 48 and 49 each of which have one end connected to opposite endsof the base member 47 and extend upwardly therefrom to join at aconnection to the respective pipe sections 39 whereby the pipe sectionsare at the apex of a triangle formed by the base member 47 and the sidemembers 48 and 49.

It is preferred to use standard lengths of pipe and the number of pipesections may vary according to the spacing between the mobile frames 3and preferably use either three or four pipe sections. In theillustrated mobile unit, there are three pipe sections 39 with a centertruss frame 30 suitably mounted on the center pipe section 39, as by apipe clamp 51 bolted on the center pipe section intermediate the endsthereof. End truss frames 52 are similarly mounted on the end pipesections 39 intermediate the. ends thereof, as by pipe clamps 53.Intermediate truss frames 54 each have the apex thereof bolted to theend flanges 40 of the center pipe section 39.

The tension members 45 and 46 are illustrated as a plurality of elongaterod sections wherein a center rod section 55 engages a respectiveU-shaped rod keeper 56 positioned at opposite ends of the center frame50 and is suitably retained therein, as by a bolt 57 extending throughlegs 58 of the U- shaped keeper 56. Opposite end portions of each centerrod section 55 are mounted in respective frame clamps 59 on oppositeends of the base member 47 of the intermediate truss frames 54. Theframe clamps 59 each have a substantially U- shaped fixed member 60mounted on opposite ends of the intermediate truss frames 54 and asubstantially U-shaped adjustable member 61 adapted to retain arespective end portion of the center rod section 55 and an adjacentoverlapping end portion of an end rod section 62. Bolts 63 extendthrough the U-shaped fixed member 60 and the U-shaped adjustable member61 whereby the adjustable member 61 is moved toward the fixed member 60to retain the respective overlapping end portions of the rod sections 55and 62 in clamping engagement therebetween. Each end rod section 62engages a respective rod keeper 64 on opposite ends of the end trussframes 52 and is suitable retained therein, as by a bolt 65 extendingthrough legs 66 of the respective rod keeper 64. The other end of theend rod section 62 is clampingly engaged in a respective rod connectorclamp 67. The rod connector clamps 67 are similar to the frame clamps 59and each have U-shaped adjustable sections 68 and 69 which are movabletoward each other by tightening bolts 70 to clampingly engage an endportion of an end rod section 62 and an end portion of a mounting rod71. A pair of the mounting rods 71 are mounted on the one side of theunit frame 8 and a pair of the mounting rods 71 at the other end of thetruss structure 4 are mounted on a flange 72 ofa slip joint pipe tocomplete the truss structure.

Irrigation fluid within the irrigation pipe sections 39 tends to deflectsame downwardly thereby tilting the unit frame 8 toward the one sidehaving the one end of the irrigation pipe 2 mounted thereon. It is,therefore, desirable to adjust the tension members 45 and 46 to camberor upwardly bow the irrigation pipe 2 while same is empty to therebyresist downward deflection under weight of the irrigation fluid. This isaccomplished by adjusting the end portions of the center rod sections 55and the end rod sections 62 in the respective frame clamps 59 and therod connector clamps 67.

It is also desirable to provide additional bracing members 73 extendingbetween the unit frame 8 and the end pipe section 39 to assist inmaintaining the mobile frame in a substantially upright position. in theillustrated structure, the bracing members 73 each have a lower endmounted at one of the opposite ends of the base member 9 of the unitframe 8 and an upper end mounted on opposite sides of a pipe clamp 74positioned adjacent the pipe clamp 53 having the end frame 52 dependingtherefrom.

The pipe clamp 74 has upper and lower clamping portions 75 and 76respectively held in clamping engagement with the pipe 3, by bolts 77.Arms 78 extend outwardly from one of the clamping portions, preferablythe lower clamping portion 76 and each arm 78 has a bore therein toreceive the upper end of the respective bracing member 73. The upperends of the bracing members 73 are threaded to receive suitabletightening devices, such as nuts 79, positioned on opposite sides ofeach of the arms 78 whereby the bracing members 73 are adjustable toconform to the camber in the irrigation pipe 3.

The self-propelled irrigation system travels over uneven terrain,therefore, it is necessary for the slip or expansion joint 6 to permitrelative movement between adjacent mobile units. The slope of theterrain may cause one mobile unit to tend to travel faster or slowerthan adjacent mobile units and the terrain may also cause one mobileunit to move radially toward or away from adjacent mobile units. Theslip or expansion joint 6 is particularly adapted to permit relativemovement between adjacent mobile units and to permit extension orcontraction of the irrigation system.

The illustrated slip or expansion joint 6 is formed by an elongatetubular sleeve member 80 mounted adjacent the apex of the unit frame 8and the sleeve member 80 has one end communicating with the irrigationpipe 2 and one end of the slip joint pipe 5 is movably received therein.Suitable fluid tight closure means engage the other side of the unitframe 8 and an exterior surface of the slip joint pipe 5 to therebypermit movement of the slip joint pipe relative to the unit frame 8while maintaining the irrigation fluid within the respective pipes. Inthe illustrated structure, a collar 81 is suitably mounted on the otherside of the unit frame 8 in an aligned relation with the other end ofthe sleeve member 80, as by a plurality of circumferentially spacedbolts 82. Fluidtight seal means, such as a rubber lip seal member 83, ismounted in the collar 81 and adapted to engage the exterior surface ofthe slip joint pipe 5. The flange 72' on the other end of the slip jointpipe 5' is adapted to have the mounting rods 71 of an adjacent mobileunit 1 mounted thereon to complete a truss structure 4 thereof.

It is necessary to maintain the one end of the slip joint pipe 5' withinthe sleeve member 80 while permitting relative movement between themobile unit 1 and adjacent mobile units 1. Therefore, suitable movementlimiting means is mounted on the other side of the unit frame 8 and isengageable with the flange 72' on the other end of the slip joint pipe 5and the movement limiting means is illustrated as an elongate bar or rod84 having one end pivotally mounted on the other side of the unit frame8 and the other end thereof extending through the flange 72 whereby theflange may move relative to longitudinally spaced abutment members 85and 86 mounted on the bar or rod 84 and positioned on opposite sides ofthe flange 72'. An arm 87 is suitably mounted on the other side of theunit frame 8, as by welding, and extends outwardly therefrom to receivea pivot pin or bolt 88 extending through the one end of the bar or rod84 and one end of a clevis bar 89 mounted on the bar or rod 84 andpositioned to have the arm 87 between the bar or rod 84 and the clevisbar 89. The abutment members 85 and 86 are illustrated as removablemounted bolts and nuts whereby the slip joint pipe 5 may be easilymounted in the sleeve member 80.

The mobile unit 1 is particularly adaptable for use in selfpropelledirrigation systems having a plurality of similar mobile units whereinthe mobile units travel over uneven terrain which results in adjacentmobile units being at different relative levels and traveling atdifferent relative speeds whereby the mobile unit 1 may lead or trailadjacent mobile units 1'. The slip or expansion joint 6 permits thisrelative movement while the bar or rod 84 maintains the one end of theslip joint pipe 5' within the sleeve member 80.

It is to be understood that while I have illustrated and described oneform of my invention it is not to be limited to the specific form orarrangement of parts herein described and shown lclaim:

1. A mobile unit for self-propelled irrigation systems having aplurality of mobile units, each of said mobile units comprismg:

a. an elongate unit frame having a flow passage extending transverselytherethrough; Y i

b. a pair of longitudinally spaced ground engaging elements;

c. a pair of longitudinally spaced yokes mounted on said unit frame andeach of said yokes engaging one of said ground engaging elements; t

d. a first elongate irrigation pipe having one end fixed to said unitframe and extending transversely outwardly from one side thereof, saidpipe being in communication with saidflow passage in said unit frame;

. a second irrigation pipe having one end communicating withsaid flowpassage and extending outwardly relative the unitframe in opposedrelation to said first irrigation plpe; I means on said unit framemovable supporting said one end of the second irrigation pipe andproviding a liquid seal therewith for flow of liquid from one pipe tothe other;

g. means connected to the unit frame and said second irrigation pipe tolimit relative movement thereof;

h. elongate truss means for supporting said first'irrigation pipe; and

i. drive means operatively engaged with said ing elements for drivingthe mo ile unit.

2. The mobile unit as set forth in claim 1 wherein:

a. said flow passage is an elongate tubular sleeve member groundengagmounted in said unit frame, said tubular sleeve member ing movementof said second irrigation pipe relative to said unit frame. 7

3. A mobile unit for self-propelled irrigation systems having aplurality of mobile units, each mobile unit comprising:

a. a substantially triangular unit frame having an elongate base memberand elongate side members;

b. a yoke mounted on each endof said base members and dependingtherefrom;

c. a wheel rotatably mounted on each of said yokes;

d. an elongate sleeve member mounted in an apex of said unit frame andextending'transversely thereof and forming a liquid passage;

. a first elongate irrigation pipe extending transversely from one sideof said unit frame, said irrigation pipe having one end fixed in liquidtight relation to said unit frame at said apex thereof in communicationwith one end of said sleeve member;

f. a collar mounted on an other side of said unit frame in an alignedliquidtight relation with an other end of said sleeve member; a f

g. a second irrigation pipe having an end portion received within saidother end of said sleeve member'forswinging and endwise movementrelative thereto;

h. fluid tight seal means mounted in said collar and engaging anexterior surface of said end rigation pipe; i. connector means on saidsecond irrigation pipe spaced from said unit frame;

portion of the secondirj. rod means pivotally connected relative to theunit frame and having spaced stops engageable with the connector meansin response to endwise movement of the second irrigation pipe toward andaway from the unit frame to limit said endwise movement while permittingswinging movement of said second irrigation pipe;

k. truss means below said first irrigation pipe and connected theretowith one 'end of said truss means connected to said unit frame forsupporting said first irrigation pipe; and

1. drive means operatively engaged with each of said wheels for drivingthe mobile unit.

4. A moblle unit for self-propelled irrigation systems having aplurality of mobile units, each of said mobile units comprismg:

a. an elongate unit frame;

b. a pair of longitudinally spaced ground engaging elements;

c. a pair elements; longitudinally spaced yokes mounted on said unitframe and each of said yokes engaging one of said ground engagingelements; v

d. an elongate irrigation pipemounted on and extending transversely fromone side of said unit frame;

e. an elongate slip joint pipe movably received within said unit frameand extending transversely from the other side of said unit frame;

. means for maintaining said slip joint pipe within said unit frame; Ig. elongate truss means for supporting'said first irrigation pipeincluding a plurality of elongate truss frames mounted on said firstirrigation pipe, said truss frames being substantially parallel withsaid unit frame and spaced along said first irrigation pipe, a pair ofelongate tension members supported at opposite ends of each of saidtruss frames, one end of each of said tension members being connected tosaid one side of said unit frame, the other end of each'of said tensionmembers being positioned to be connectedto a slip joint pipe of anadjacent mobile unit in the irrigation system; and

h. drive means operatively engaged with said ground engaging elementsfor driving the mobile unit.

5. The mobile unit as set forth in claim 4 including:

a. a pipe clamp mounted on said irrigation pipe intermediate the endsthereof; and

b. a pair of elongate bracing members each having one'end mounted onsaid pipe clamp and the other end thereof mounted on said unit frame.

' 6. The mobile unit as set forth in claim 4, wherein:

' a. said truss frames are each substantially triangular shapedstructures each having an elongate base member and elongate sidemembers;

b.'said irrigation pipe engages said triangular truss frames at the apexthereof; and

c. said tension members engage said truss frames at opposite ends ofsaid base member whereby said truss means is positioned below saidirrigation pipe.

7. The mobile unit as set forth in claim 6, wherein:

a. said tension members are elongate truss rods;

' b. said, truss rods each have a plurality of rod sections which haveend portions positioned in overlying adjustable rela- -tion whereby saidirrigation pipe can be upwardly bowed while empty to resist downwarddeflection under weight of irrigation fluid.

1. A mobile unit for self-propelled irrigation systems having aplurality of mobile units, each of said mobile units comprising: a. anelongate unit frame having a flow passage extending transverselytherethrough; b. a pair of longitudinally spaced ground engagingelements; c. a pair of longitudinally spaced yokes mounted on said unitframe and each of said yokes engaging one of said ground engagingelements; d. a first elongate irrigation pipe having one end fixed tosaid unit frame and extending transversely outwardly from one sidethereof, said pipe being in communication with said flow passage in saidunit frame; e. a second irrigation pipe having one end communicatingwith said flow passage and extending outwardly relative the unit framein opposed relation to said first irrigation pipe; f. means on said unitframe movable supporting said one end of the second irrigation pipe andproviding a liquid seal therewith for flow of liquid from one pipe tothe other; g. means connected to the unit frame and said secondirrigation pipe to limit relative movement thereof; h. elongate trussmeans for supporting said first irrigation pipe; and i. drive meansoperatively engaged with said ground engaging elements for driving themobile unit.
 2. The mobile unit as set forth in claim 1 wherein: a. saidflow passage is an elongate tubular sleeve member mounted in said unitframe, said tubular sleeve member being larger in diameteR than saidfirst and second irrigation pipes, said second irrigation pipe havingsaid one end extending into said sleeve member; and b. said meanssupporting said one end of the second irrigation pipe being closuremeans engaging said other side of said unit frame in liquid tightrelation and having a resilient seal member engaging an exterior surfaceof said second irrigation pipe for permitting endwise and swingingmovement of said second irrigation pipe relative to said unit frame. 3.A mobile unit for self-propelled irrigation systems having a pluralityof mobile units, each mobile unit comprising: a. a substantiallytriangular unit frame having an elongate base member and elongate sidemembers; b. a yoke mounted on each end of said base members anddepending therefrom; c. a wheel rotatably mounted on each of said yokes;d. an elongate sleeve member mounted in an apex of said unit frame andextending transversely thereof and forming a liquid passage; e. a firstelongate irrigation pipe extending transversely from one side of saidunit frame, said irrigation pipe having one end fixed in liquid tightrelation to said unit frame at said apex thereof in communication withone end of said sleeve member; f. a collar mounted on an other side ofsaid unit frame in an aligned liquidtight relation with an other end ofsaid sleeve member; g. a second irrigation pipe having an end portionreceived within said other end of said sleeve member for swinging andendwise movement relative thereto; h. fluid tight seal means mounted insaid collar and engaging an exterior surface of said end portion of thesecond irrigation pipe; i. connector means on said second irrigationpipe spaced from said unit frame; j. rod means pivotally connectedrelative to the unit frame and having spaced stops engageable with theconnector means in response to endwise movement of the second irrigationpipe toward and away from the unit frame to limit said endwise movementwhile permitting swinging movement of said second irrigation pipe; k.truss means below said first irrigation pipe and connected thereto withone end of said truss means connected to said unit frame for supportingsaid first irrigation pipe; and l. drive means operatively engaged witheach of said wheels for driving the mobile unit.
 4. A mobile unit forself-propelled irrigation systems having a plurality of mobile units,each of said mobile units comprising: a. an elongate unit frame; b. apair of longitudinally spaced ground engaging elements; c. a pairelements; longitudinally spaced yokes mounted on said unit frame andeach of said yokes engaging one of said ground engaging elements; d. anelongate irrigation pipe mounted on and extending transversely from oneside of said unit frame; e. an elongate slip joint pipe movably receivedwithin said unit frame and extending transversely from the other side ofsaid unit frame; f. means for maintaining said slip joint pipe withinsaid unit frame; g. elongate truss means for supporting said firstirrigation pipe including a plurality of elongate truss frames mountedon said first irrigation pipe, said truss frames being substantiallyparallel with said unit frame and spaced along said first irrigationpipe, a pair of elongate tension members supported at opposite ends ofeach of said truss frames, one end of each of said tension members beingconnected to said one side of said unit frame, the other end of each ofsaid tension members being positioned to be connected to a slip jointpipe of an adjacent mobile unit in the irrigation system; and h. drivemeans operatively engaged with said ground engaging elements for drivingthe mobile unit.
 5. The mobile unit as set forth in claim 4 including:a. a pipe clamp mounted on said irrigation pipe intermediate the endsthereof; and b. a pair of elongate bracing members each having one endmounted on said pipe clamp and the other end Thereof mounted on saidunit frame.
 6. The mobile unit as set forth in claim 4, wherein: a. saidtruss frames are each substantially triangular shaped structures eachhaving an elongate base member and elongate side members; b. saidirrigation pipe engages said triangular truss frames at the apexthereof; and c. said tension members engage said truss frames atopposite ends of said base member whereby said truss means is positionedbelow said irrigation pipe.
 7. The mobile unit as set forth in claim 6,wherein: a. said tension members are elongate truss rods; b. said trussrods each have a plurality of rod sections which have end portionspositioned in overlying adjustable relation whereby said irrigation pipecan be upwardly bowed while empty to resist downward deflection underweight of irrigation fluid.